The present invention relates to similarity measures used for measuring the degree of match of data sets to each other.
There are many fields in which it is desirable to be able to measure the similarity or degree of match of one data set to another. For example, there are many situations in which two images are compared to determine a spatial transformation which relates the two images. For example, one method of compressing a time sequence of images is to detect movement vectors which describe where image features found in a first frame are positioned in a second frame. Alternatively, in the field of medical imaging, it is often desirable to display two images of the same object (for example, part of a patient's body) overlying one another. The two images could be images taken at different times or images taken with different modalities. The display of the two images overlying one another requires them to be registered and this involves finding the position of corresponding image features in each of the images. Similar techniques are useful in other fields involving so-called data fusion, for example in which a visible or infra-red image is registered with a different kind of image, such as synthetic aperture radar. The need may also arise with one-dimensional signals such as ECG and blood-oxygen level which could usefully be registered, and four-dimensional images such as contrast-enhanced MRI in which a 3-D image varies over time.